A motor vehicle commonly includes a catalyst (also referred to herein as a catalytic converter) as an engine exhaust after-treatment device. However, at engine start, particularly during cold ambient conditions, the catalyst has not yet reached its optimal operating temperature (e.g., light-off temperature). Exhaust released before the catalyst has reached its light-off temperature may contribute a large percentage of the total vehicle emissions. Accordingly, engine control systems may use various approaches to expedite catalyst heating to reduce an amount of time after engine start before the catalyst light-off temperature is reached, thereby reducing vehicle emissions. Typically, the various approaches aim to increase an amount of thermal energy that reaches the catalyst, such as by increasing exhaust temperature via retarded spark timing.
However, the inventor herein has recognized an additional approach to further reduce the amount of time after engine start before the catalyst light-off temperature is reached. Namely, the inventor herein has recognized that the magnetocaloric effect (MCE) may be used to decrease an amount of thermal energy needed to achieve the catalyst light-off temperature, which may be used alone or in combination with other approaches for expediting catalyst heating, by decreasing a specific heat capacity of the catalyst. As one example, retarded spark timing may reduce fuel economy, decrease combustion stability, and increase engine vibrations, and thus, decreasing spark retard usage may increase fuel economy and reduce an occurrence of misfire.
Further still, the MCE may be used to thermally regulate other vehicle system components, such as braking system components (e.g., brake rotors). Typically, to increase brake cooling, the size of the brake rotors is increased. Increasing the size of the brake rotors increases the heat capacity and surface area of the rotors, which enables the braking system to absorb more thermal energy before the temperature increases and dissipate that thermal energy faster. However, increasing the size of the brake rotors also adds unsprung, rotating mass to the vehicle. The inventors herein have recognized that by using the MCE to decrease the specific heat capacity of the brake rotors, the rate at which the braking system dissipates heats to the surroundings may be increased without increasing the size of the brake rotors.
In one example, the issues described above may be addressed by a method for an engine, comprising: responsive to a temperature of an exhaust catalytic converter being below a first threshold temperature, applying a magnetic field to an exhaust system component arranged proximate to the exhaust catalytic converter; and, responsive to the temperature increasing to or above the first threshold temperature, stopping applying the magnetic field. In this way, the amount of time before the exhaust catalytic converter reaches its light-off temperature may be reduced.
As one example, such as when the temperature of the exhaust catalytic converter is less than a second, lower threshold temperature, an alternate engine parameter may be adjusted in addition to applying the magnetic field to the exhaust system component, such as retarding spark timing. In this way, the temperature of the exhaust catalytic converter may be raised faster than when spark retard or the magnetic field are used alone, further reducing the amount of time before the exhaust catalytic converter reaches its light-off temperature and, as a result, reducing vehicle emissions. As another example, the method may further include applying the magnetic field to a braking system component of a vehicle in which the engine is installed for a duration following a vehicle braking event; and stopping applying the magnetic field to the braking system component in response to one or more of a temperature of the braking system component reaching a threshold temperature and commencement of a subsequent braking event. By applying the magnetic field to the braking system component following braking, heat may be dissipated from the braking system while keeping the braking system smaller, preventing braking system degradation due to overheating while reducing the overall mass of the vehicle.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.